Microsoft on Saturday disabled the search tool on its Safety & Security Center after attackers poisoned results with links to pornographic URLs.

The company restored the website's search field early Monday afternoon ET, and later apologized to users for the gaffe.

On Friday, Alex Eckelberry, the general manager of GFI Software's security group and the CEO of Sunbelt Software, said that searches using terms like "sex," "porn," "girl" and "streaming" on the Microsoft site were returning links to pornographic websites at or near the top of the results list.

Microsoft's Safety and Security Center is a consumer-oriented resource for Windows users, and includes security news and links to tools such as the company's free antivirus software, Security Essentials.

Although search poisoning is not unusual -- it's a well-worn tactic by those hoping to spread malware and dupe users into visiting scamming sites -- this is different, said Eckelberry.

"This is crafty," Eckelberry said today in an interview. "This isn't normal search poisoning. It's poisoning the results with actual searches. Users were getting back a prior search as a search result."

Eckelberry speculated that the Microsoft site had been saving searches, probably because it allowed users to forward searches to others using Twitter.

If Eckelberry is on target, the scammers used the Microsoft site's Twitter feature to create a large number of searches that led to their preferred destination URLs, in this case links to what Eckelberry called "hardcore, seriously hardcore porn sites."

By repeatedly searching for sites using pre-selected phrases -- "sex" and "girl," for example -- on the Safety & Security Center, criminals tricked the site into saving those searches, which then popped up near the top of the results of any subsequent searches by others.

"They used the site's unique ability to save a search against the site," he said.

Eckelberry said it was the first time he had seen a saved search feature poisoned this way.

Microsoft appears to have purged the site's saved search list of the dangerous links.

A search early Monday on Google, for instance, using "sex site:Microsoft.com," returned a long list that included pornographic pages, all with the title "Microsoft Security Search Results." By mid-day, however, the same search on Google brought up fewer porn sites, and none with the "Microsoft Security Search Results" heading.

The restored search tool also no longer brings up porn pages when searches are conducted using the same words and phrases that resulted in dodgy links over the weekend.

Around 2 p.m. ET, Microsoft confirmed the poisoning and apologized for the problem, but declined to answer questions about how scammers had infiltrated the search results.

On July 8, Microsoft became aware of a search poisoning issue affecting the Safety & Security Center site," said Bryan Nairn, a senior manager with the company's Trustworthy Computing group, in an emailed statement. "Microsoft quickly removed the search tool and resolved the issue. We apologize for any inconvenience this may have caused for visitors to the website."

"This isn't a slam on Microsoft; they have some very, very sharp guys on security," said Eckelberry. "But by trying to make [the Safety & Security Center site] somewhat social, it blew up in their faces."

The problem isn't limited to pornography: Such sites are often also used to spread malware.

"Inevitably, these types of things can lead to malware," Eckelberry said.